1. Field of the Invention
The present invention relates to an optical disk discrimination method for recording/reproducing information to/from multiple types of optical disks by using an optical pickup and an optical disc device using the method.
2. Description of the related art
In recent years, optical disks as disc-shaped recording media have been in general use as an external storage device of a personal computer. Such optical disks are available in a variety of types including a CD initially developed for the purpose of appreciation of music, a CD-R, a CD-RW, a DVD-ROM, a DVD-R, a DVD±RW, a DVD-RAM, and a Blu-ray Disc (hereinafter also referred to as a BD) developed for recording of data on personal computers. An optical disk device that supports these optical disks is designed so that multiple optical disks can be used on a single optical disk device. This means that an optical disk must have a feature to detect the type of an optical disk mounted on the optical disk.
With these optical disks, the emission wavelength of laser beams used for recording/reproducing data differs between a CD system a DVD system and a BD system. The corresponding optical system differs according. It is thus important to discriminate the type of an optical disk mounted on an optical disk device.
A related art optical disk device that supports both the CD system and the DVD system will be described referring to FIG. 9.
FIG. 9 is a block diagram of the pickup controller of an optical disk device. In FIG. 9, a numeral 1 represents an optical disk, 2 a pickup module, 3 a spindle motor, 4 an optical pickup, 5 a carriage, 6 a feed part, 7 a feed motor, 8 an analog signal processor, 9 a servo processor, 10 a motor driving part, 11 a digital signal processor, 12 a laser driving part, and 13 a controller.
Operation of a pickup controller thus configured in the related art will be described.
In FIG. 9, the pickup module 2 is composed of the spindle motor 3 for rotating the optical disk 1, the optical pickup 4 for reading an information signal from the optical disk 1, and the feed part 6 for moving in the radial direction of the optical disk 1 the carriage 5 where the optical pickup 4 is mounted. The analog signal processor 8 generates a focus error signal and a tracking error signal based on signal output from an optical sensor (not shown) inside the optical pickup 4 in the carriage 5 provided inside the pickup module 2 and outputs the signals to the servo processor 9.
The focus error signal indicates a displacement of a light beam spot emitted from an objective lens (not shown) included in the optical pickup 4 from the recording surface of the optical disk 1 in the focal direction. The tracking error signal indicates a displacement of the optical spot from the information track of the optical disk 1 in the radial direction of the optical disk.
The analog signal processor 8 generates a lens position signal indicating the relative positions of the objective lens and the carriage 5 by extracting the low range components of a tracking error signal.
The servo processor 9 is composed of an ON/OFF circuit, an arithmetic circuit, a filter circuit and an amplifier circuit. The servo processor 9 performs focus/tracking control over the objective lens so that the light beam spot will trace the information track of the optical disk, and performs feed control so that the objective lens will maintain an almost neutral position by using the low range components of the tracking error signal. The feed part 6 is composed of a feed motor 7, a gear (not shown), and a screw shaft (not shown). When the feed part 6 rotates the feed motor 7, the carriage 5 moves as a feed motor pulse is periodically outputted from the feed motor 7. The controller 13 controls the entirety of thus configured servo part.
FIG. 10 is a block diagram of the focus control system of a related art optical disk device.
In FIG. 10, a numeral 14 represents an objective lens, 15 a half mirror, 16 a division sensor, 17 a head amplifier, 18 a differential amplifier, 19 a division sensor, 20 a head amplifier, 21 a differential amplifier, 22 a selector switch, 23 a filter, 24 a selector switch, and 25 a driving circuit.
Operation of a focus control system of an optical disk device thus configured will be described. To discriminate the type of an optical disk, generally laser beams having a longer wavelength for CDs are irradiated first and laser beams having a shorter wavelength for DVDs are irradiated next in consideration of the difference in the optical power level.
When laser beams for CDs are irradiated, light reflected on the reflecting surface of the optical disk 1 in FIG. 10 reaches the half mirror 15 via the objective lens 14. For example, light for CDs passes through the half mirror 15 and impinges on the division sensor 16 and gain-adjusted by the head amplifier 17. Differential arithmetic operation is made by the differential amplifier 18 on a signal from the head amplifier 17 to generate a focus error signal related to laser beams for CDs are used.
The focus error signal thus generated that is related to laser beams for CDs are used as a signal to pass through the selector switch 22 and control a focus actuator via the filter 23, selector switch 24, and driving circuit 25.
The focus error signal is transmitted to the controller 13 for the controller 13 to control focus driving.
Next, an exemplary method for discriminating the type of an optical disk mounted will be described.
FIG. 11 is an explanatory drawing to discriminate the type of an optical disk.
As shown in FIG. 11, the objective lens is brought closer to a recording surface from a distance to the optical disk. A focus error signal (FE signal) is detected and the detected s-curve characteristic and added value FS of the FE signal are obtained. The CD system or DVD system is determined as follows: when the normalized FE amplitude value shown in FIG. 11 is greater than a threshold, a CD disk is assumed; when the value is smaller than a threshold, a DVD disk is assumed.
FIG. 12 shows normalized FE amplitude values by optical disk type and optical disk device.
As shown in FIG. 12, it is possible to set a threshold for a normalized FE amplitude value and use the threshold to discriminate between optical CD disks and optical DVD disks. When the detected normalized FE amplitude value is greater than the threshold, a CD disc is assumed. When the value is smaller, a DVD disk is assumed.
A technique to discriminate the type of an optical disk is described on Patent Reference 1.
Patent Reference 1: JP-A-2005-85351
However, there are some cases where a CD disk and a DVD disk cannot discerned using a threshold specified based on a normalized FE amplitude value due to variations in the assembly of optical components of optical disk devices or variations in the manufacture of optical disks.
FIG. 13 represents normalized FE amplitude values corresponding to several types of optical disks.
Part A in FIG. 13 corresponds to an optical disk device that determines a DVD disk as a CD disk because the s-curve amplitude value of the focus error of DVD is large. Part B in FIG. 13 corresponds to an optical disk device that determines a CD disk as a DVD disk because the s-curve amplitude value of CD is small.
In this way, each of the optical disk devices is accompanied by variations in the manufacture of optical components and amplitude of s-curve characteristic of a focus error signal. This results in failure to discriminate between CD disks and DVD disks.